1. Field of the Invention
The present invention relates to a charge-pump circuitry, and more particularly, to a charge-pump circuitry which directly outputs a target voltage.
2. Description of the Related Art
It is common that a system comprises multiple ICs which provide different functions, and some IC can operate normally only under a voltage potential higher than the external voltage source provided to the system. Therefore, it is common that the system uses a charge-pump circuitry to pull up the voltage potential of the external voltage source to a voltage potential required by these special ICs for supporting the normal operation of these ICs.
FIG. 1A is a schematic circuit diagram of a conventional regulated charge-pump circuitry. Referring to FIG. 1A, the conventional regulated charge-pump circuitry is composed of a voltage multiplier module 100 and an operational amplifier 109. The voltage multiplier module 100 comprises dual port switches 101, 103, 105, 107 and capacitors 111, 113. Wherein, two terminals of the capacitor 111 electrically couple to the dual port switch 101 and the dual port switch 103, respectively. One terminal of the dual port switch 101, which is disposed opposite to the capacitor 111, receives an external voltage source VDD, and one terminal of the dual port switch 103 opposite to the capacitor 111 is grounded. One terminal of the dual port switch 105 electrically couples to the capacitor 111 and the dual port switch 101, and the other terminal of the dual port switch 105 electrically couples to the capacitor 113 and a voltage regulator 110 which is composed of the operational amplifier 109. One terminal of the dual port switch 107 electrically couples to the capacitor 111 and the dual port switch 103, and the other terminal of the dual port switch 107 receives the external voltage source VDD.
Referring to FIG. 1A, the “turn-on” cycles of the dual port switch 101, 103 are the same and not overlapped with the “turn-on” cycles of the dual port switch 105, 107. In addition, the “turn-on” cycle of the dual port switch 107 leads the “turn-on” cycle of the dual port switch 105 a certain period of time. When the dual port switches 101, 103 are turned on, the capacitor 111 is being charged to a potential of the external voltage source VDD. After the charge of the capacitor 111 is completed, the dual port switches 101, 103 are turned off. Then, the dual port switch 107 is turned on first, and the dual port switch 105 is turned on subsequently. Meanwhile, the voltage potential on a positive voltage terminal 13 of the capacitor 111 is two times of the potential of the external voltage source VDD, and the voltage is entirely charged to the capacitor 113.
Referring to FIG. 1A, an example is used for explanation hereinafter. It is assumed that the external voltage source VDD is 4V, and finally the target voltage output from the output terminal Vout is 5V. The voltage multiplier module in the conventional regulated charge-pump circuitry of FIG. 1A pulls up the external voltage source VDD from 4V to 8V first, and sends the pulled-up voltage to the voltage regulator 110, and a 5V voltage is output from the output terminal Vout via the voltage regulator 110. Therefore, in theory, the optimum efficiency of the conventional regulated charge-pump circuitry is 62.5% (i.e. 5V/8V=0.625). In other words, only 5V out of 8V is used, and the rest 3V is wasted.
FIG. 1B is a schematic circuit diagram of another conventional regulated charge-pump circuitry. Referring to the circuit diagram in FIG. 1B, a comparator 121 is used to replace the operational amplifier 109 in FIG. 1A. This conventional regulated charge-pump circuitry is characterized in that a control signal is output from an output terminal of the comparator 121 for controlling the dual port switches 101, 103, 105, 107. Its operating principle is similar to the conventional regulated charge-pump circuitry in FIG. 1A. More particularly, when the capacitor 111 has been charged to the voltage potential of the external voltage source VDD, the comparator 121 controls the dual port switches 101, 103 to turn off, and when the voltage potential on the output terminal Vout reaches the target voltage, the comparator 121 sends out a control signal to control the dual port switches 105, 107 to turn off. Thus, in theory, no power is wasted on the output terminal. However, when all dual port switches 101, 103, 105, 107 are turned off, there may be still some charges remaining inside the capacitor 111. Since these charges are totally isolated in the capacitor 111 and cannot not be discharged even when time passed by, a power loss is generated accordingly.
In summary, the conventional regulated charge-pump circuitry uses a voltage multiplier module to pull up an external voltage source first, and the pulled-up voltage is then sent to a voltage regulator for generating a target voltage.